The use of inks is well known throughout a variety of industries. For instance, in the cosmetic industry various products such as eyeliner, eyeshadow pencils, lipstick, emollients, toners, and certain other types of cosmetic compositions call for the use of some form of colorant such as an ink or at least one pigment and/or a dye. The insoluble pigments, including the noncertifiable inorganic types as well as those classified within the broader category of certified organic pigments are the most widely used colorants. Depending upon the desired finished cosmetic product, the inks or combinations thereof are incorporated within the particular formulations by grinding, dispersing, mixing, and, at times, extended by use of mechanical apparatus such as hammer mills, roller mills, ball mills, colloid mills, mortars, micropulverizers, and any other suitable conventional means. Regardless of the ink or suitable derivative thereof selected and the means of incorporation utilized therefor, the suitability of the particular colorant is determined by the intended use of the final product.
In order to be useful in the preparation of cosmetic products, the selected ink(s) must exhibit particularly desired physical and chemical characteristics. Among these characteristics of greatest concern are included light and pH stability, good resistance to oxidizing and reducing, as well as to alkali and weak acids, and dispersibility, particularly, grindibility. The latter three interrelated characteristics are of most particular interest, because they impart the desired results of dispersibility, uniformity and smoothness in the finished product, when applied to the skin of the consumer.
Some pigment particles within the ink, due to their inability to be "wetted down" by the ointment, are incapable of yielding a desired uniform, if not homogeneous, final composition. In such cases, the pigment base contains particles which tend to float to the top thereby resulting in a non-uniform composition which is unappealing to the consumer. This problem can sometimes be remedied by the incorporation of minute quantities of organic pigments. However, the addition of organic pigments tends to yield an undesirably more intense color, upon application. Oftentimes, as a result of their inherent indispersibility, the use of certain pigment bases such as, in particular, those utilized in eyeliner and eyeshadow pencil formulations, result in undesirable entrapment of air bubbles. This problem can usually be overcome by heating the mixture to approximately 70.degree. Centigrade under slow stirring. Since the determination as to complete evacuation of air bubbles is virtually a matter of periodic "pulldown", i.e., smear testing, on a glass slide or a piece of paper, the foregoing combined heat and stir method of removing entrapped air bubbles presents the trial and error risk problem of possible inadvertent prolonged heating and excessive agitation. Also, it is obvious that any additional remedial steps can ultimately become time consuming and therefore somewhat costly.
A yet further problem often encountered in the use of certain pigment-base inks is that of undesirable color change of the particles, due to inherent structural alteration during milling. For instance, ferrous oxide tends to lighten to a dark-brownish shade. This phenomenon occurs as a result of the temperature increase during milling. Hence, there is a widespread need, particularly, in the cosmetic industry, for a method wherein smaller pigment particles can be obtained to circumvent the problems of the prior art. Accordingly, it is desirable to provide a pigment-base ink which is void of the above-mentioned drawbacks, yet foreseeably useful in virtually all industrial applications wherein conventional inks are called for.
It is an object of this invention to provide a method for the polymeric encapsulation of unusually smaller, uniform pigment-base particles.
It is a further object of this invention to provide an improved pigment-based ink which exhibits the desired properties of increased wettability, i.e., dispersibility, and heat resistance, with concommittant color stability.
It is also a further object of this invention to provide an improved pigment-based ink which is particularly useful throughout, but not limited to, the cosmetic industry.
It is a still further object of this invention to provide improved cosmetic products, due to the incorporation therein of inks having polymer encapsulated pigment particles therein which were prepared, in accordance with this invention.